Added EBNF-like grammar for mojom as documentation.
Added EBNF-like grammar for mojom as documentation.

Had to violate EBNF to include regular expression for some complex tokens.

The production rules can likely be simplified further by taking more advantage
of EBNF repetition, option etc, but this should be an accurate description.

Fixes #67

R=rudominer@chromium.org

Review URL: https://codereview.chromium.org/1011913003

chinmaygarde/mojo,jianglu/mojo,afandria/mojo,chinmaygarde/mojo,collinjackson/mojo,chinmaygarde/mojo,afandria/mojo,jianglu/mojo,collinjackson/mojo,jianglu/mojo,afandria/mojo,chinmaygarde/mojo,jianglu/mojo,jianglu/mojo,collinjackson/mojo,chinmaygarde/mojo,afandria/mojo,chinmaygarde/mojo,chinmaygarde/mojo,afandria/mojo,jianglu/mojo,afandria/mojo,jianglu/mojo,chinmaygarde/mojo,collinjackson/mojo,afandria/mojo,collinjackson/mojo,jianglu/mojo,chinmaygarde/mojo,collinjackson/mojo,afandria/mojo,collinjackson/mojo,collinjackson/mojo,collinjackson/mojo